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Date: Thu, 16 Jul 2009 14:49:02 +0800
From: Eugene Teo <>
CC: "Steven M. Christey" <>
Subject: CVE-2009-1895 kernel: personality: fix PER_CLEAR_ON_SETID

Reported by Julien Tinnes.

"We have found that the current PER_CLEAR_ON_SETID mask on Linux doesn't


We believe it is important to add MMAP_PAGE_ZERO, because by using this
personality it is possible to have the first page mapped inside a
process running as setuid root.  This could be used in those scenarios:

- Exploiting a NULL pointer dereference issue in a setuid root binary
- Bypassing the mmap_min_addr restrictions of the Linux kernel: by
running a setuid binary that would drop privileges before giving us
control back (for instance by loading a user-supplied library), we could
get the first page mapped in a process we control.  By further using
mremap and mprotect on this mapping, we can then completely bypass the
mmap_min_addr restrictions.

Less importantly, we believe ADDR_COMPAT_LAYOUT should also be added
since on x86 32bits it will in practice disable most of the address
space layout randomization (only the stack will remain randomized)."

Upstream commit:


Thanks, Eugene

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